8.19—Inserting recombinant DNA into cells

A recombinant plasmid or vector must enter a suitable host cell. Selection or screening distinguishes cells that received the construct, after which expression and product quality can be tested.

Transformation is only the entry step: culture conditions, selectable markers, gene orientation and host machinery affect whether the target protein is made.

A bacterial colony carrying the plasmid may grow on selective medium, but protein assays are still needed to show that the inserted gene is expressed correctly.

Antibiotic resistance as a marker does not prove therapeutic protein production, and a vector is not itself the finished medicine.